Balance the following equations. (Use the lowest possible coefficients. These may be zero.)
(a) As(s) + ClO3-(aq) ---> H3AsO3(aq) + HClO(aq) (acidic solution)
I am using half-reactions but I don't really get this at all. Can someone explain?
acidic solution means H+ is available.
4H+ + ClO3- + As(s)>>H3AsO3 + HClO3
Sure! Balancing equations using half-reactions is a common method in chemical reactions, especially in redox reactions. Here's a step-by-step explanation of how to balance the given equation:
Step 1: Identify the oxidation and reduction half-reactions.
In this equation, the atoms As and Cl change their oxidation states. As gets reduced, while Cl gets oxidized.
Step 2: Write the half-reactions.
a) Oxidation half-reaction: ClO3- --> ClO
b) Reduction half-reaction: As --> H3AsO3
Step 3: Balance the atoms other than oxygen and hydrogen in each half-reaction.
a) In the oxidation half-reaction, there is one Cl on the left side, but only one Cl on the right side. Therefore, it is already balanced.
b) In the reduction half-reaction, there is one As on the left side, but three As on the right side. So, we need to balance it by adding a coefficient of 3 in front of As on the left side.
Step 4: Balance oxygen atoms by adding water molecules (H2O).
a) In the oxidation half-reaction, there are three oxygen atoms on the left side and only one on the right side. So, we need to add two water molecules (H2O) on the right side of the equation.
b) In the reduction half-reaction, there are zero oxygen atoms on the left side. So, we need to add three water molecules (H2O) on the left side of the equation.
Step 5: Balance hydrogen atoms by adding hydrogen ions (H+).
a) In the oxidation half-reaction, there are zero hydrogen atoms on both sides. So, we don't need to add any hydrogen ions.
b) In the reduction half-reaction, there are six hydrogen atoms on the right side and zero on the left side. So, we need to add six hydrogen ions (H+) on the left side of the equation.
Step 6: Balance the charges by adding electrons (e-).
a) In the oxidation half-reaction, the total charge on the left side is -1. On the right side, there are two chloride ions (Cl-) with a total charge of -2. In acidic solution, we add H+ ions to balance the charge, so we can add two H+ ions on the right side. Therefore, we also need to add two electrons (e-) on the left side to balance the charges.
b) In the reduction half-reaction, there are three hydrogen ions (H+) with a total charge of +3 on the left side and zero charge on the right side. So, we don't need to add any electrons.
Step 7: Multiply the half-reactions by appropriate coefficients to balance the number of electrons transferred.
a) In order to make the electrons equal in both half-reactions, we multiply the reduction half-reaction by two. This gives us:
2As + 6H2O ---> 2H3AsO3 + 6H+
b) By doing this, we also multiply the number of As atoms by two. So, the balanced equation becomes:
2As(s) + 6ClO3-(aq) ---> 2H3AsO3(aq) + 6HClO(aq)
The equation is now fully balanced with the lowest possible coefficients.